Chapter 11: Nutrition and Energy Balance in Active People

Photo 11-1  Fruits and Vegetables.  photo by Brian R. MacIntosh

Case Presentation

Multi-Stage Events: Highlighting Nutritional Needs for Cyclists in the Tour de France

The Tour de France is one of the most challenging cycling races in the world. It began in 1903 by a sport newspaper called L’Auto and has increased in popularity ever since. In July of every year, athletes pedal 3500 km through France and neighbouring European countries, competing to win the yellow jersey. Over three weeks, these athletes race 21 different stages, ranging from shorter time-trial to gruelling hill climbing days. On the longer days, competitors will cycle for more than 200 km over high mountain passes. All of this with only two days of rest!

 

The difference between winning and losing is measured in seconds, and proper nutrition and hydration can make or break the race (Saris, van Erp-Baart et al., 1989). These athletes need to consume thousands of kilocalories (kcal) each day and drink enough to replenish fluids and electrolytes; all while riding a bike for hours. Once the current day’s stage is completed, they need to recover and prepare for the next day. Chris is an international level cyclist who is competing in the Tour de France for the first time. Let us follow Chris as he prepares for and completes today’s ride and recovers for tomorrow.

The Importance of Nutrition for Physical Performance

One of the most important nutritional considerations for athletes is their energy needs. All of the body’s energy for physical activity comes from the macronutrients: carbohydrates, fat, and protein. Athletes in the Tour will need between 6000 and 7000 per day. Chris knows that if he doesn’t consume enough carbohydrates his blood glucose levels will drop. When this happened to him in the past, he felt dizzy, confused, irritable, and tired and couldn’t finish his race. Athletes often call this bonking. Chris is also aware that he has to match his water and electrolyte intake with his sweat rate. In a previous race, he did not hydrate properly and became dehydrated. Consequently, he had a very poor performance and developed heat exhaustion. We will discuss all of the nutrients required for physical performance later in the chapter but let’s take a look at Chris’ needs right now.

Pre-Event

Chris’ goal with his pre-event nutrition is to optimize his body’s carbohydrate and fluid levels to ensure that he has enough energy to finish the race and avoid dehydration. He also wants to make sure that the food he eats is easily digestible and familiar to him. He doesn’t want to end up with stomach cramps or digestive distress from trying all sort of new local cuisine. In previous training sessions, he developed routines for his meals and has tested everything to make sure it works for him. This is not the time to experiment with deep-fried frog legs!

Pre-Event Energy and Fluid Intakes

Chris knows that he needs to maximize glycogen, the body’s carbohydrate stores, at every opportunity. Three hours before the start of today’s stage, Chris will eat a full meal that is high in carbohydrates and contains some protein. About an hour before the race starts, he is also going to have a pre-race snack including some carbohydrates and fluids. Meal timing is very important, if he waits too long, he won’t have enough energy for the race, but if he eats too close to the start time, all of that undigested food could cause an upset stomach.

Chris has checked the weather forecast and knows that the temperature on the course tomorrow will range from 20-30^oC. He has also looked at the racecourse and estimates that it will take him 5 hours to finish. He has been drinking water and sports drinks as often as he can since he finished riding yesterday and has been adding extra salt to his meals. He’s making sure that he is well hydrated prior to starting the race and can confirm his hydration status by checking that his urine is pale yellow and voluminous.

During Event

Nutritional intakes during a long-distance endurance event are extremely important. Even with the best pre-event nutrition, it is not possible to exercise for hours without giving your body some additional carbohydrates and fluids. Chris has carefully prepared all of the food and fluids that he will be able to pick up along the way. Chris will try to match his fluid intakes with his sweat rate, however, knows this can be challenging, so is aiming to avoid losing greater than 2% body weight. Additionally, he will consume up to 90g carbohydrate per hour of endurance exercise. Including some protein in combination with his carbohydrate intake may also be beneficial. Therefore, Chris will consume a maximum of 450 g of carbohydrate (1800 kcal) during the event.

During Event Energy and Fluid Intakes

While racing, Chris will have a sports drink that provides him with water, electrolytes, and contains 6-8% carbohydrates. During the race, Chris will alternate between drinking water and a sports drink. Liquid forms of energy digest quickly and easily and will provide him with immediate energy. The carbohydrates and electrolytes in the sports drink will also help his body absorb the water more effectively. He will also eat some easily digestible solid foods containing some protein or sports gels and wash them down with plenty of water. In multi-day events, it is especially important to consume carbohydrates during exercise, as your body stores are continually being depleted as you compete.

Post Event

After today’s sprint to the finish, Chris knows that no matter how tired he is he must start thinking about tomorrow’s stage. He has a small window of opportunity to maximize his recovery. Exercise increases sensitivity and depletes muscle glycogen, which means after exercise Chris will be better able to refuel his muscles. He can use the increased insulin sensitivity to maximize glucose and amino acid delivery to the muscles, helping replenish the muscles’ energy and aiding in rebuilding of the tissue. He should be sure to consume lots of carbohydrates and some protein in the 4 hours after exercise to maximize this effect. After that, the second phase of recovery begins and he should be sure to eat a healthy meal high in carbohydrates with protein. If he does not follow this recovery plan, he will not be able to optimize glycogen re-synthesis and give his body the protein it needs to build and repair muscles.

Post Event Energy and Fluid Intakes

Immediately after his race, Chris is going to have some fluid, carbohydrates, and protein in the form of a recovery drink. In the next couple of hours, he is also going to eat a full meal that is high in carbohydrates and contains protein.

Chris has been drinking throughout the day but knows that with a long ride, in the heat, he has likely not replaced all of the fluid and electrolytes he’s lost. After his race, he is going to weigh himself and compare with his prerace weight to determine how much body water he has lost. He will continue to drink until he has made up the lost water weight. He will also consume some sports drinks or electrolyte drinks and salty foods to replace his electrolytes.

This case study has provided a general overview of nutrition and meal timing for athletes engaged in multi-day endurance events. In this chapter, we will go into much more detail and provide specific guidelines for athletes and individuals who are physically active.

Introduction

Since the beginning of competitive sports, athletes have recognized the relationship between nutrition and performance. Dating as far back as the ancient Olympics, there are numerous accounts of athletes consuming foods and beverages to specifically improve their performance. Milo of Croton, a great wrestler who won his events at 5 consecutive Olympics (532-526BC), was said to eat 20 pounds of meat, 20 pounds of bread, and 18 pints of wine per day! Although the validity of this is questionable (~55,000 kilocalories per day!), it highlights the long-standing and ever-changing fascination with nutrition and athletic performance. More recent examples of athletes’ use of nutrition to improve performance are plentiful. In more modern Olympic times (early 1900s), there is documented evidence of the consumption of 22 glasses of beer and a half bottle of wine by a German 100km walker during his race. Reports of marathon runners who consumed cognac, prior to and during their event, seem bizarre in the context of our modern-day sport nutrition principles! Although slightly different in nature, there are many familiar examples of current nutritional practices for improved performance. Fitness enthusiasts and athletes alike consume various whole foods and natural health products in an attempt to optimize wellness and performance. Examples of current popular nutritional ergogenic aids include creatine, antioxidants, caffeine, fish oils, and consumption of protein drinks (Grandjean, 1997).

Throughout history, the number of anecdotal and in some cases factual examples of nutritional practices intended to boost performance has been plentiful. Given the barrage of advertisements and ‘free advice’ given to athletes, it can be challenging to confidently identify the best dietary choices for improving performance. Importantly, the science of sport nutrition has grown tremendously in recent decades and recommendations based on scientific evidence can now be provided to athletes – both professional and amateur. This chapter will emphasize evidence based nutritional guidelines and best practices for both physically active populations and athletes to help them reach their full athletic potential.

The purpose of this chapter is to introduce the field of nutrition in relation to healthy active living and peak sports performance. Herein we will briefly describe the physical activity-specific role of carbohydrates,  protein, water, vitamins, and minerals and then highlight special nutritional requirements for active living and optimal athletic performance. This chapter has been split into two defined sections. The first section will provide foundational information about nutrition and discuss nutrition in the context of ‘healthy active living’ for the fitness enthusiast. The second half of the chapter will be geared towards the competitive amateur to professional athlete and provide specific guidelines for nutritional practices that optimize performance.

The Nutrients: Fuel for Performance

The foods and beverages that we consume are composed of six categories of nutrients that are critical for life that include carbohydrates,  protein,  vitamins, and minerals, and water. These are classified as essential nutrients and we cannot survive without adequate consumption of each category. The six essential nutrients provide us with energy; allow for growth and development; maintenance of body homeostasis; prevention of disease; as well as many other critical bodily functions. In the context of physical activity and athletic performance, essential nutrients provide the energy and chemicals to promote optimal physical functioning as well as appropriate adaptation to training.

In the human body, we have many varied sources of energy for physical activity. Carbohydrate energy is largely in the form of blood glucose and liver and muscle glycogen; a large reserve of stored energy in the form of fat is found in adipose tissue and intramuscular fat; and while we would prefer not to use body protein for energy, certain amino acids can be converted to glucose when needed and thereby provide energy for exercise. Understanding the macronutrient composition of our foods is critical in understanding how dietary energy is used and converted to physical energy. Following digestion, absorption, and assimilation of nutrients, we convert carbohydrates, protein, and fat into a usable form of energy – adenosine triphosphate (ATP) – via various metabolic pathways. We have two primary energy systems that allow us to perform work: the anaerobic system and the aerobic system. While both systems are typically active simultaneously, the intensity and duration of the exercise, the fitness level of the individual, and the environmental temperature will influence which system preferentially supplies the majority of fuel and the mixture of substrates that will be used. The immediate, short-term and long-term energy systems and the fuels required are described below.

Energy Systems and Nutrient Use

The direct role that specialized nutrition plays in modifying the ATP –creatine phosphate system (ATP-CP), also known as the immediate energy system, is likely small. The best way to increase available ATP from the ATP-CP system is likely via a power-specific training program and adequate overall nutrition. However, a popular dietary supplement, creatine has been demonstrated to improve repeated sprint performance.

The other energy systems: glycolysis, tricarboxylic acid cycle (TCA), and the electron transport chain (ETC) all require adequate nutrition for production. In order for glycolysis to occur, adequate carbohydrates (blood glucose and muscle glycogen) must be available. Glucose can be degraded to pyruvate and then acetyl CoA which is a frequently-used substrate for the TCA. Acetyl CoA, the starting substrate for the TCA, can also be generated from fat and protein (Figure 11-1). Protein is broken down into amino acids, deaminated or transaminated, and then the remaining keto-acid enters the TCA. Likewise, fatty acids are broken down into two carbon units via beta oxidation, and enter the TCA. Consequently, the TCA is a highly integrative pathway that incorporates all substrates (carbohydrates, protein, and fat) to produce usable ATP. In addition to macronutrients, the TCA requires vitamins, and minerals to function adequately. Certain micronutrients, including the B-vitamins, magnesium (Mg²⁺), and iron (Fe⁺) are critical in the production of ATP (Figure 11-1).

How the Energy Systems Work Together

As an individual begins to exercise, all three energy systems begin replacing ATP-CP (immediate), glycolysis, leading to the formation of lactate (short-term energy system), and aerobic metabolism (long-term energy system). These systems are described further in Chapter 6. As exercise continues, there is an increase in breathing and heart rate, supporting the increase in aerobic metabolism. At lower intensities of physical activity, when the duration of exercise is prolonged, the preferential fuel for the TCA is fat. The complete oxidation of, for example a common fatty acid, palmitic acid will yield 106 ATP (Darvey, 1998). The potential energy from each substrate can also be expressed as the caloric equivalent, which for fat is ~4.65 kcal· L^-1 of oxygen and represents the energy available per litre of oxygen consumed. As the intensity of exercise increases, the body uses a greater proportion of carbohydrates. The complete oxidation of glucose to carbon dioxide and water yields 30 to 36 ATP depending on the shuttle used to oxidize NADH. The potential energy from carbohydrates expressed as a caloric equivalent is ~5 kcal · L^-1 of oxygen consumed. While there is not a great deal of variation between the substrates, the caloric equivalent values do indicate that carbohydrate is the most efficient in the use of oxygen to provide energy. In summary, a physically active individual requires a calorically adequate and balanced diet to fuel activity and to achieve optimum athletic performance. Specific macronutrient and micronutrient requirements are provided in the subsequent sections.

Macronutrients

Carbohydrates, protein, and are the three essential, energy-providing macronutrients. These macronutrients provide energy in the form of a kilocalorie (kcal). A is a measurement of food energy and is equivalent to the amount of heat required to increase the temperature of 1 kg of water by 1°C. We must consume a certain amount of kcal from a combination of these macronutrients to ensure adequate overall energy for physical activity and for optimal athletic performance. Energy needs of individuals vary greatly and depend on sex, age, physical activity levels, body composition, height, and genetics. Over consumption or under consumption of any macronutrient can be detrimental to wellness and performance. Moreover, it is important to consider the type of each macronutrient that is consumed, as there are various qualities of carbohydrates, protein, and fat that can invariably influence health and athletic capability. The following section will examine each macronutrient and how consumption can influence physical activity and optimum sports performance. The recommendations for physically active individuals will be provided first while the specific nutritional recommendations for peak athletic performance will be addressed during the second half of the chapter.

What are you Eating?

Food labels are an excellent way to determine the nutrients you are consuming (Figure 11-2). In Canada, all foods and beverages, excluding fresh meats and produce, must contain information on a defined set of nutrients (Canada, 2018). Many different dietary patterns can provide the energy and nutrients an individual needs for health and performance. One option is Canada’s Food Guide (CFG), which provides guidance on food choices for all Canadians and can easily be adapted for physically active and athletic populations. Another more detailed method of determining what you are eating is to use dietary analysis software. There are many software programs available that allow you to enter the foods and beverages you consume and determine the nutritional breakdown. The Dietitians of Canada provide a free program at eaTracker.ca that is useful in personal dietary assessments.

Carbohydrates

Dietary carbohydrates, (4 kcal/g) are the primary source of fuel for most people – both sedentary and active. The average Canadian consumes approximately 50% of their energy in the form of carbohydrates (Canada, 2017). The acceptable macronutrient distribution range (AMDR) represents a range of intakes that are associated with reduced risk of chronic disease while providing all the essential nutrients. For carbohydrates, this acceptable range is 45-65% of total daily calories. Adequate intake of carbohydrates is critical for both health and optimal performance because of their key role in meeting energy requirements, protein sparing, and for fueling the central nervous system. Rich sources of carbohydrates include grains, starchy vegetables, legumes, juices, fruits, and sports drinks. Dietary fibre, an indigestible form of carbohydrate is also required in an amount of 38 g · d^-1 for males aged 19-50 and 25 g· d^-1 for females aged 19-50 years. In addition to promoting digestive system function, consuming adequate fibre has also been shown to help prevent certain chronic diseases such as type 2 diabetes and cardiovascular diseases (Slavin, 2013).

Carbohydrates can be divided into two categories, based on chemical structure: simple and complex. Simple carbohydrates come in two forms: monosaccharides (glucose, fructose, and galactose) and disaccharides (sucrose, maltose and lactose), whereas a complex carbohydrate is a polysaccharide [polymer of >2 carbohydrate molecules (starch and dietary fibre)]. Dietary carbohydrates are a key energy source for physical activity. When we consume carbohydrates – either simple or complex – digestive enzymes in the mouth, stomach, and small intestine break them down into absorbable monosaccharides such as glucose and fructose. Monosaccharides cross the intestinal wall and are transported to the liver via the hepatic portal system. Once at the liver, monosaccharides other than glucose are converted to glucose. Then glucose is either stored as glycogen or released into the systemic blood circulation. This causes a rise in blood glucose that will gradually decrease back to baseline levels as working tissues such as the brain, kidneys, muscle, and heart utilize the glucose. To gain entry into these cells, a glucose transporter (GLUT) must transport glucose across the cell membrane. Once in the cell, glucose has one of two fats – immediate energy use or storage. In muscle, liver, and heart, glucose can be stored as glycogen or converted to fat for storage as adipose tissue. In all other tissues, excess glucose is converted to fat and stored as adipose.

Fuel for muscle contraction is particularly important for physically active individuals and athletes; therefore, we will examine the fate of glucose in a muscle cell. After a meal, circulating blood glucose enters skeletal muscle via GLUT1 or GLUT4. Once in the cell cytosol, hexokinase converts glucose to glucose-6-phosphate (G6P). G6P can either be channeled to glycolysis and TCA or be used as the starting product of glycogen synthesis. Therefore, during periods of immediate energy need (i.e. physical activity), glucose can be used for production of for muscle contraction, but in times of recovery, glucose can be stored as glycogen for future energy demands. The ability of the body to store extra glucose in the form of glycogen is important for fueling future physical activity. However, we have only finite capacity for glycogen storage and once those depots are at capacity [80g-100 g (320 kcal-400 kcal) in the form of liver glycogen and 300g-400 g (1200 kcal-1600 kcal) as muscle glycogen] extra glucose is converted to fatty acids and stored as fat if the body does not need the glucose to meet energy needs (Burke, Hawley et al., 2011). During exercise, blood flow to the muscle increases and GLUT4 translocates to the muscle surface membrane. As the exercise continues, blood glucose or the stored muscle glycogen can be utilized for production. Glycolysis and subsequent β- oxidation represent the major fate of glucose in the muscle (Rose and Richter, 2005).

Glycemic index

Glycemic index (GI) is a tool used to classify carbohydrates according to their impact on blood glucose. The concept of was developed by a Canadian researcher and classifies foods based the rate at which postprandial blood glucose increases when compared to 50 g of glucose (Table 7.1) (Jenkins,Wolever et al., 1981). In general, 50 g portions of each test food are used to make this comparison. Foods with a high GI cause higher levels of postprandial blood glucose, whereas foods with a low GI result in lower postprandial blood glucose. Generally, foods that contain simple sugars tend to raise blood glucose more rapidly and those that contain complex carbohydrates tend to raise blood glucose more slowly due to the slower rate of digestion and absorption (Mondazzi and Arcelli, 2009, Qin,Wang et al., 2017). The GI can be important to athletes and physically active individuals because it influences both blood glucose and glycogen storage capacity. Athletes and physically active individuals can use the GI to optimize their performance. For example, during an event an athlete would want to choose a food that is high on the GI because this will immediately replace glucose that is being used for physical activity (Gretebeck, Gretebeck et al., 2002). Another example of when an athlete would want to eat a high GI food is after exercise to replace the glycogen stores in the muscle and liver. However, prior to exercise, low GI foods would be recommended to stabilize blood glucose levels (Burdon, Spronk et al., 2017, Heung-Sang Wong, Sun et al. 2017). On a day-to-day basis, however, everyone – athlete or not – should try to eat foods lower on the GI to provide their body with a stable supply of glucose and reduce their risk for chronic diseases such as type 2 diabetes.

≤55 Low GI, 56-69 Medium GI, ≥70 High GI. Generally, grain products have the highest whereas legumes, nuts, and vegetables have lower GI. Based on Atkinson et al. (Atkinson, Foster-Powell et al., 2008) and Gretebeck et al. (Gretebeck, Gretebeck et al., 2002)

Carbohydrate Requirements for Physically Active Individuals

The timing of carbohydrate intake is critical for all physically active individuals as it influences carbohydrate fuel availability. It is important to consume carbohydrates prior to exercise to ensure adequate glycogen storage in the liver and muscles. As well, if exercise duration is over 1-2 hours, it is important to consume carbohydrates during exercise to maintain blood glucose levels and reduce fatigue. It is important to note that liver glycogen and muscle glycogen have different fates. The primary substrate responsible for maintenance of blood glucose during fasting or exercise is liver glycogen. This occurs via a series of hormonal controls that regulate release of liver glycogen into the blood to maintain normal blood glucose. In contrast, muscle glycogen is only used as a fuel for production in the skeletal muscle.

As you recall, the AMDR for carbohydrate is 45-65% of daily calories, however, recommendations for athletes based on their body weight are thought to better reflect their needs. Specifically, athletes should strive for 3-12 g of carbohydrates per kg of body weight to ensure adequate energy for training and performance. The range reflects variations in duration and intensity of activity. In general, as the intensity and duration increase there is a greater need for carbohydrates (Thomas, Erdman et al., 2016). Overall, a diet rich in carbohydrates derived from complex, unprocessed sources is most likely to improve health while still providing appropriate fuel.

Problems of Inadequate Carbohydrate Intake

A typical North American diet will provide sufficient carbohydrate  to fuel moderate to high intensity physical activity lasting up to 2 hours. However, the length of time that an athlete can perform at a given intensity is related to the size of glycogen stores and is affected by previous nutrition and exercise patterns. The point at which muscle glycogen stores are depleted during physical activity is sometimes referred to as ‘hitting the wall’. When an individual hits the wall, they feel fatigued and must slow the intensity of their exercise in order to switch to a greater proportion of for fuel. If an individual continues to exercise after hitting the wall, without replenishing carbohydrates, they will eventually ‘bonk’. Bonking refers to the point when both muscle and liver glycogen stores are depleted, and the athlete cannot continue with exercise. Endurance athletes may try to achieve glycogen supercompensation, maximizing glycogen storage in the muscles, by a process called carbohydrate loading. Specific carbohydrate loading protocols are outlined at the end of this chapter. As expected, carbohydrate loading is generally only applicable to activities that are longer than 2 hours. Athletes performing short, high intensity activities usually will not benefit from carbohydrate loading and may actually be hindered due to water retention. The temporary weight gain associated with carbohydrate loading is the consequence of water retention related to the storage of ~3 grams of water with each gram of glycogen.

Conclusions

In conclusion, a physically active individual requires a diet that contains 45-65% of their daily calories from carbohydrates to fuel the activity. Specific carbohydrate requirements for athletes in heavy training for peak performance and competition will be discussed at the end of this chapter.

Protein

Protein intake is arguably one of the most controversial topics in sports nutrition. There has been long-standing interest in the consumption of protein for optimal performance, with many athletes believing that more is always better. The purpose of this section is to provide information about protein use in the body and include evidence-based recommendations for protein intake.

Dietary proteins consist of chains of amino acids and provide 4 kcal · g^-1 of energy. There are 20 amino acids; 9 are essential and 11 are considered nonessential. Nonessential amino acids can be synthesized in the body, whereas essential amino acids cannot be synthesized, so they need to be consumed. Dietary protein has many functions in the body including energy supply and production of proteins (hormones, transporters, enzymes, muscle, hair, etc.). Upon digestion and absorption, amino acids are mainly used to build structural and functional proteins in the body but can also be metabolized for energy. The nitrogen-containing amino group is removed from the amino acid (deamination) and the remaining carbon skeleton (keto-acid) enters the TCA (Figure 11-1). Depending on the specific amino acid, they enter the TCA at various levels and result in aerobic production. As with excess carbohydrate intake, excess amino acids can be converted to and eventually get stored as adipose tissue. During rest, approximately 5% of energy is derived from protein. The magnitude of protein’s contribution to energy needs during exercise depends on the intensity and duration of the activity as well as how much fuel in the form of carbohydrate and fat is available.

Protein Requirements for Physically Active Individuals

The adult AMDR for protein is 10-35% of daily energy intake or can be calculated based on body weight using a value of 0.8 grams protein per kg body weight. For example, a sedentary individual who weighs 80 kg should aim to consume 80 kg∙0.8 g/kg = 64 g of protein per day. The daily dietary protein requirements of a physically active individual will vary depending on their level of physical activity and type of activity. Protein needs are increased with exercise for three primary reasons:

• increases to muscle mass following heavy strength training;
• for muscle recovery and repair;
• to compensate for protein used as energy during training when carbohydrates are limited.

As with carbohydrates, protein recommendations based on body weight are thought to best match an athlete’s needs. Athletes require 1.2-2.0 g of protein · kg^-1 body weight depending on their training and energy needs (Thomas, Erdman et al., 2016).

Dietary Sources of Protein

The quality of a protein source depends on the amino acids and digestibility. Animal sources of protein generally provide the full complement of essential amino acids and are easily digestible, thus they are classified as complete and high-quality proteins. Animal proteins include milk, eggs, meat, poultry, cheese, and fish. Protein is also available from plant-sources and includes legumes, beans, and grains. In general, plant-based proteins are considered incomplete because they do not contain sufficient quantities of one or more of the essential amino acids such as lysine, methionine, or tryptophan. Grains generally do not contain adequate lysine and legumes do not contain adequate methionine or tryptophan. If an athlete is consuming a vegetarian diet or a diet that primarily consists of only plant-based proteins, it is important to combine a grain and a legume to ensure that a complete array of amino acids is consumed. These foods are referred to as ‘proteins’. For example, together chickpeas (hummus) and pita bread provide complete protein and are complementary; likewise, rice and beans, or lentil soup and bread. For a vegetarian, it is important to consume proteins over the period of a day – the sources do not need to be at a single meal. It is perfectly healthy to be a vegetarian athlete, however, care must be taken to ensure adequate intake of all essential amino acids (adequate protein) and other at-risk nutrients such as iron, zinc, vitamin B₁₂, vitamin D and calcium among others (Melina, Craig et al., 2016).

Protein and Amino acid Supplementation

The use of protein supplements (i.e. whey protein or soy protein shakes) and individual amino acids as ergogenic aids is very popular with both recreational and professional athletes. The use of protein supplements to achieve adequate amounts of protein intake is well supported, as whey and soy are both high quality proteins. However, most Canadians – both male and female – do not require protein supplementation given that protein intake as part of our whole-foods diet generally exceeds recommended amounts. Moreover, there is no evidence to suggest that a diet with excess protein is necessary or beneficial. The specific timing and intake recommendations are highlighted in the second half of this chapter. Furthermore, scientific evidence does not currently support the use of individual amino acids as ergogenic aids for athletes or fitness enthusiasts. Supplementation with single amino acids can disrupt the balance of essential amino acids and inadvertently result in deficiency (Phillips, Moore et al., 2007).

Fats

Dietary s are the most energy dense macronutrient at 9 kcal · g^-1 and fat storage in the body provides humans with our largest reservoir of energy. As recommended by the AMDR, the optimal diet contains approximately 20-35% of energy from fats with no more than 10% from saturated fat. Dietary fats are critical for many functions including an important energy reserve, a source of energy at rest and during exercise, protection for vital organs, thermoregulation, a source and carrier of vitamins (vitamins A, D, E, and K) and other fat-soluble phytochemicals, hormone synthesis, and satiety.

Fats and oils are classified according to chemical structure and the two primary forms are unsaturated and saturated fats. Unsaturated fats are generally liquid at room temperature and often derived from plants such as canola, safflower, and olive. Unsaturated fats confer many health benefits such as reducing low-density lipoprotein (LDL) cholesterol levels when consumed as part of a balanced, low fat diet. Canadians eat diets that contain foods rich in two types of unsaturated fats: polyunsaturated (e.g. sunflower and corn oils) and monounsaturated fats (e.g. olive and canola oils). There are two essential fatty acids required by the body that are both unsaturated. Linoleic acid is an omega-6 fatty acid, which refers to the location of its double bond, whereas linolenic acid is an omega-3 fatty acid. Researchers are interested in the ratio of these fatty acids in our diets because evidence suggests that omega-3 have anti-inflammatory properties while omega-6 promote inflammation. The second major type of fat, saturated fats come primarily from animal fats and are solid at room temperature (e.g. meat, cheese, butter, coconut oil). Hydrogenation is a process that takes an unsaturated fat and converts it into a fat that is more saturated and contains ‘trans fat’. Trans fats are naturally found in some ruminant animal products but can also be manufactured industrially via hydrogenation for enhancement of food texture and shelf life. Industrial trans fats increase the risk of cardiovascular disease by increasing LDL cholesterol (“bad” cholesterol) levels and decreasing HDL cholesterol (“good” cholesterol) levels. For this reason, it is recommended that people avoid consuming industrial trans fats. Recommendations for consumption of total fat (20-35%), and saturated fat (<10%) are the same for all people, regardless of physical activity levels. Dietary fats are used first for physiological functions after which the excess is stored as adipose tissue.

In addition to saturated and unsaturated, we consume animal products that contain dietary cholesterol. Cholesterol is not an essential nutrient as our liver is able to make all the cholesterol we need. Cholesterol is required for many functions including hormone production and cell structure. Contrary to what you might expect, dietary cholesterol is not the only dietary factor to influence blood cholesterol levels. Individuals who are concerned about their cholesterol also need to consider their saturated fats, dietary fibre, and trans fat intakes. Nonetheless, intake of cholesterol should be limited to 300 mg for all individuals – both sedentary and active.

During physical activity, use is mostly dependent on carbohydrate availability and intensity of exercise. When carbohydrates are readily available, one can perform exercise at a higher intensity due to ease of production; however, upon depletion of carbohydrate stores, the intensity of exercise must be reduced, and fat utilized for energy. Fatty acids undergo beta oxidation to be broken down into 2-carbon units for entry into the TCA (Figure 11-1). Although the body has a vast reserve of stored energy in the form of fat, the conversion of fat into ATP uses more energy than the conversion of carbohydrates to ATP in TCA. Furthermore, fats can only be used as a fuel source in the presence of oxygen. Therefore, the intensity of exercise must be reduced, as fat metabolism cannot supply ATP at the same rate as carbohydrate metabolism. As the body adapts to training, a greater percentage of fat can be used for fuel at a given submaximal intensity of exercise.

The Micronutrients: Vitamins and Minerals

Vitamins

The effective provision of energy and regulation of metabolic processes requires both chemical energy (carbohydrates, protein, and and a balance of vitamins and minerals. Vitamins are essential organic substances required for life and for optimal performance. Vitamins play many roles in the body including metabolic processes that release energy from food; regulation of tissue synthesis; and protection of cell membranes (Table 11-2). There are two classifications of vitamins: fat soluble (A, D, E, and K) and water-soluble (C and B’s). The fat-soluble vitamins do not dissolve easily in water or blood and require dietary fat for transport and storage. If taken in excess, fat-soluble vitamins can build up in fatty tissue and become toxic. The water-soluble vitamins in contrast readily dissolve in water and are easily transported in the blood. However, due to their water solubility, they are not stored to any great extent and turn over rapidly. Regular intake of vitamins is therefore necessary for health and performance. To understand how much of each vitamin we require, The National Academy of Medicine provides dietary reference intakes (DRI). The DRI provides information regarding recommended dietary allowance (RDA), the adequate intake (AI), and tolerable upper limit (UL) of nutrients. The RDA or AI are provided for most vitamins and represent the minimum recommended amount of each vitamin to consume on a daily basis. Some vitamins also have a UL, which is the maximum amount that one should not exceed daily. It is challenging to determine whether athletes and physically active individuals require vitamin supplementation. The vitamins that are most often a concern for athletes are the B vitamins, vitamin D, and the antioxidants (C and E). However, deficiencies are often only seen in those who consume poor, unbalanced diets or restrict their calories. Daily RDA and AI can often be achieved through consumption of a healthy and adequate-energy diet. Vitamin supplements should not be used to compensate for a poor diet, as they will not ensure adequate intake of the macronutrients, fibre, fluid and antioxidant s. Given that athletes are often consuming a large volume of food, their vitamin intake should be sufficient, if they are making healthy choices. One exception is the need for a vitamin D supplement when sunlight exposure is inadequate (winter, indoor training, etc.). Vitamin supplements do not improve performance in those who consume nutritionally adequate diets. It is recommended that individuals who would like to supplement one or more single vitamins consult with a health care professional knowledgeable in sports nutrition prior to beginning any vitamin program.

Minerals

Minerals are inorganic substances (atoms or elements) required for life in relatively small amounts. There are two classifications of minerals: major minerals and minor minerals. The seven major minerals are:

• calcium (Ca²⁺),
• chloride (Cl^–),
• magnesium (Mg²⁺),
• phosphorus (P),
• potassium (K⁺),
• sodium (Na⁺),
• sulphur (S)

For a mineral to be classified as major, intakes of greater than 100 mg per day are required. There are 14 minor minerals, which include chromium (Cr), copper (Cu), fluoride (F), iodine (I), iron (Fe), manganese (Mn), selenium (Se), and zinc (Zn). A minor mineral is required in amounts less than 100 mg per day. All minerals are consumed in our diet and then stored in our bodies. Minerals are required for matrix structures (bone/teeth); regulation of metabolism via use in enzymes and hormones; maintaining homeostasis in functions such as muscle contraction, neural function, heartbeat, and acid-base balance. A complete list of functions critical to sports performance is provided in Table 11-3. Similar to vitamins, the supplementation of single minerals is not recommended. The RDA of most minerals can be obtained from consuming a nutritionally balanced, energy-sufficient diet. The most likely minerals to be deficient in an athlete’s diet are zinc, iron, and calcium. However, as with low vitamin status, low mineral status often arises due to unbalanced diets or caloric restriction. Individuals wishing to supplement minerals should consult with a sport medicine physician prior to consumption.

Of special interest to athletes and physically active individuals, are the minerals referred to as electrolytes such as Na⁺, K⁺, Ca²⁺, and Cl^–. These minerals are electrically charged particles (ions) that are critical for ensuring proper electrochemical gradient across cells, regulation of acid-base balance, and regulation of blood volume and blood pressure. Most individuals consume sufficient quantities of these minerals; however, care should be taken if there are large fluctuations in body water – both in intake (drinking) and output (urine, sweat, breathing, and feces). Recommendations for these minerals combined with fluid intake are provided below.

Water

The human body consists of about 65-75% water. Variations in body water – either increases or decreases can lead to impairment of physiological function and in the extreme, death. Body water is vital for many functions including transport of nutrients, removal of waste, temperature regulation, and cushioning of joints. Water balance describes the flow of water into and out of the body. Intake of water comes primarily from consuming beverages and foods, but also is produced during metabolism as a byproduct. Water output is affected by losses in the urine, feces, and sweat, as well as from evaporative loss from the skin and the ventilatory system. When the losses of body water exceed the input, this leads to dehydration. Dehydration leads to decreased performance when there is a loss of body water equivalent to 2% or more of total body weight. Symptoms of dehydration can include headache, dizziness, fatigue, tachycardia, unconsciousness, and in extreme cases death. In order for an individual to determine water status, it is recommended that immediately prior to exercise and immediately following exercise, an individual weigh themselves. The change in body weight is an excellent determinant of changes in body water. In contrast, a small percentage of athletes suffer from the opposite problem and actually over-hydrate resulting in a condition called hyponatremia. Hyponatremia can result from consuming too much water without replacing electrolytes.

It is recommended that physically active individuals and athletes consume fluids prior to exercise, during exercise, and after exercise. The volume required depends on many factors including sweat rate, environment (humidity, temperature and altitude), genetics, and personal fitness levels. Drinking to thirst is often insufficient for athletes competing at high intensities in warm-hot environments. In general, in the 2-4 hours prior to exercise, individuals should consume a volume of water equivalent to 5-10 mL· kg^-1 body weight (Thomas, Erdman et al., 2016). For example, a 60 kg person should consume about 300-600 mL of fluid. This amount of fluid maximizes hydration status and reduces the risk of having to urinate during exercise. During exercise, sweat rates can vary from 0.3 to 2.4 L · kg^-1 and can contain variable amounts of Na⁺ and K⁺. Therefore, it is recommended that individuals consume fluids at a rate that maintains body weight or minimizes changes in body weight. If an event or training session is to last more than 1 hour, it is recommended that fluids (such as sports drinks) containing 6-8% carbohydrates and electrolytes (Na⁺, K⁺) be consumed instead of plain water. After exercise, it is recommended to consume 1.25 L to 1.5 L fluid for every kilogram of body weight lost during exercise for rehydration (Thomas, Erdman et al., 2016).

Energy Requirements for a Physically Active Population

Consuming enough total energy is important for all physically active individuals. In competitive sport, meeting energy needs is a key factor in optimizing athletic performance. Daily energy requirements can fluctuate widely depending on individual characteristics and physical activity levels. An athlete like Chris in the Tour de France can easily expend over 4000 per day in exercise alone, whereas a person with largely sedentary behaviour may only burn a few hundred kcal per day due to physical activity. Without adequate energy intake, the ability of the body to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue is compromised. In fact, the benefits of training can be negated if adequate energy is not consumed. In female athletes, persistent low energy intake can lead to the triad, a serious health problem that involves disordered eating, amenorrhea (loss of menstruation) and low bone mass.

One of the major reasons that individuals increase or decrease their energy intake is to change their body weight or more specifically their body composition. Weight management through exercise is a chief goal of many fitness enthusiasts. For example, Paula is in her first year of university and finds that she has gained a couple kilograms of weight during her first semester. While she hasn’t really changed her eating habits very much compared to when she was in high school, she finds that she is less active throughout the day sitting in class and studying in the evenings. Paula decides that she is going to keep her dietary habits fairly similar but burn more energy by walking to university each day. Paula will change her energy balance by increasing her energy expenditure and keeping her energy intake relatively stable. If Paula is 66 kg when she starts walking to and from university every day, she will expend approximately 5.9 kcal·min^-1 if she walks at a pace of 4.0 miles per hour (6.4 km·hr^-1). Her walk takes 60 minutes total each day resulting in 354 kcal·day^-1 energy usage. If she is persistent, Paula might expect to lose approximately 1 pound (0.6 kg) of body weight after approximately 10 days according to popular thinking about energy deficits. However, the body likes to protect a higher body weight and may make metabolic adaptations so that weight loss is not guaranteed in a linear manner with an energy deficit. Even if Paula does experience some weight loss, it is critical to realize that weight loss will not continue indefinitely because as Paula’s weight drops, the cost of doing the same exercise goes down. Therefore, if she has not reached her goal weight when the weight loss plateaus, she will have to increase the duration or intensity of her walk or consume fewer calories to continue to create an energy deficit.

For athletes, the incentive to change their overall energy intake or individual macronutrient intake is often linked to a desire for less mass and greater lean mass. Achieving what is perceived as an optimal body composition is often undertaken in hopes of gaining a competitive edge. Consuming enough energy is critical if these compositional changes are to take place in a positive direction. For example, David thinks that if he could increase his muscle mass and decrease his fat mass he would be more competitive in triathlons. David decides he will consume more protein to help build up muscle, but restrict his overall energy intake in hopes of losing fat. This strategy could end up working against David. When overall calories are restricted too severely, both fat and lean tissue can be used as a fuel by the body (Stiegler and Cunliffe, 2006). For example, if a person simply restricts their calories, the weight loss that results is approximately 75% adipose tissue and 25% fat free mass. If the person also exercises while they restrict their calorie intake, the loss of fat free mass can be reduced to 12% (Weinheimer, Sands et al. 2010). If David restricts his eating too much, the lean tissue he was hoping to build up may be used as a fuel source by his body to meet its daily energy needs. This loss of lean tissue can compromise many processes in his body including his immune, endocrine and musculoskeletal function and result in loss of strength and endurance.

You can recognize the importance of understanding what the energy requirements of the body are. Knowing how to accurately estimate your energy needs is key to understanding how to achieve or maintain a healthy and optimal body weight.

Energy Needs: What, Why, and How They Change

Energy balance occurs when energy intake equals energy expenditure. Body weight reflects energy balance and will remain stable when an individual is in energy balance; it will increase when a person is in positive energy balance; and it will decrease when a person is in negative energy balance. Energy intake is simply reflected in the kilocalories a person consumes throughout the day. If you recall, carbohydrates and protein  supply the body with 4 kcal·g^-1 while provides 9 kcal·g^-1 and alcohol 7 kcal·g^-1 Food records, where a person records all foods and beverages consumed over a 3 or 7-day period, and 24-hour dietary recalls are common ways of estimating a person’s energy intake. The energy intakes of athletes tend to be higher than sedentary individuals to balance the higher energy expenditure associated with their training.

Energy expenditure is the second component of energy balance. The major components of energy expenditure include resting metabolic rate (RMR), physical activity, and the thermic effect of food (TEF) (Figure 11.3) (Levine, 2005). RMR is synonymous with resting energy expenditure and is usually the largest portion of daily energy expenditure. RMR is the energy required to fuel basic physiologic functions in the body, including circulation, respiration, nervous system function, and organ function. RMR is measured usually after 4 hours of resting. For most individuals, RMR will account for about 60-75% of total daily energy expenditure. Higher levels of lean body mass in athletes are often associated with higher RMR largely because lean tissue is more metabolically active than adipose tissue. Many factors can increase or decrease RMR (Figure 11-3).

• For most individuals, the energy cost of physical activity is the second largest contributor to energy expenditure. For some athletes their training can be so extensive that the energy they expend in physical activity can actually equal or exceed their RMR. The energy cost of performing activity is influenced to a large extent by body weight. For example, while a 57 kg person running at 9.6 km∙hr^-1 expends 568 in an hour, a 91 kg person would expend 909 kcal running at the same speed (Ainsworth, Haskell et al., 2000). Although there is some variability, due to differences in economy, the energy cost of running can be estimated as 1 kcal∙kg^–1∙km^-1.

The body also uses energy to digest, absorb and metabolize the foods we eat. This is called the thermic effect of food (TEF) and it accounts for approximately 10% of total daily energy expenditure. This means that if a person consumes 3500 kcal · day^-1, approximately 350 will be used to process the food they eat. There is some difference in the TEF between the macronutrients and it requires more calories to assimilate protein and carbohydrates than fat.

Equations for Calculating Energy Needs

Several methods are available to estimate daily energy expenditure. The most accurate is through the use of direct calorimetry, which directly measures the body’s heat production in a small room, called a calorimeter. Because these chambers are expensive and not readily available outside of research settings, indirect calorimetry is an acceptable option in real life situations. Indirect calorimetry is based on equations that predict energy expenditure based on the input of variables such as age, weight, and height. Three equations are presented below. The Harris-Benedict equation is commonly used to predict resting energy expenditure and has distinct equations for males and females (Figure 11-4) (Harris and Benedict, 1919). Beyond estimates of RMR, specific activity factors can be used to arrive at total daily energy expenditure. For example, the Dietary reference intakes (DRI) Method uses an estimate of RMR plus a physical activity factor to arrive at an estimate of 24-hour energy needs (Figure 11-4) (Lupton, Brooks et al., 2002). For athletes it is important to remember that these equations were developed with the general population and may not apply specifically to athletes. The equations provide a good estimate of energy requirements, but athletes will have to do some fine-tuning to arrive at their optimal energy needs. This is because athletes often have higher RMR due to increased lean body mass and for the DRI Method, the physical activity component may be much higher than expected in an athletic population (Ainsworth, Haskell et al., 2000). It is also important to note that physical activity often varies from day-to-day in an athlete’s training and their energy intake needs to fluctuate accordingly. Finally, to compensate for differences in individuals with overweight or obesity, a different equation called the Mifflin-St. Jeor has been shown to be more accurate for predicting RMR adults with overweight or obesity (Figure 11-4) (Frankenfield, Roth-Yousey et al., 2005).

Figure 11-4

Indirect calorimeter metabolic rate calculations.

Harris-Benedict Equation

Adult Females:

Resting energy expenditure = 655 + 9.6 ·(weight in kg) + 1.8 ·(height in cm) – 4.7 ·(age)

Adult Males:

Resting energy expenditure = 66 + 13.7 ·(weight in kg) + 5.0 ç(height in cm) – 6.8 ·(age)

Dietary reference intake (DRI) Method

Adult Females:

354 – 6.91 · (age) + (9.36 · [weight in kg] + 726∙[height in meters])

Where Physical activity (PA): Sedentary 1.0, Low active 1.12, Active 1.27, and Very active 1.45

Adult Males:

662 – 9.53 · (age) +∙(15.91 · [weight in kg] + 539.6∙[height in meters])

Where Physical activity (PA): Sedentary 1.0, Low active 1.11, Active 1.25, and Very active 1.48

Mifflin-St. Jeor Equation

Men: (9.99∙kg) + (6.25∙cm) – (4.92∙years) + 5

Women: (9.99∙kg) + (6.25∙cm) – (4.92∙years) – 161

How to Incorporate an Active Lifestyle for Weight Loss/Maintenance for Populations with Obesity

Obesity rates continue to rise worldwide and place an ever-increasing burden on health care systems. Treatment programs aimed at increasing energy expenditure and decreasing energy intake are very often effective at helping individuals lose weight but maintaining that weight loss is continually problematic. Several research studies have tried to determine what it is about successful weight loss maintainers that allows them to succeed when so many regain the weight they lost. Researchers found that being able to persist in key behaviour changes, including reducing calorie intake, increasing physical activity and monitoring their weight, were all important to keeping the weight off (Wing and Phelan, 2005). Other researchers have looked at psychological and behavioural factors that help weight loss maintainers succeed and found the following (Soleymani, Daniel et al., 2016):

• Physically active for an average of 1 hr·d^-1
• Low-calorie, low diet
• Self-monitored physical activity and diet
• Ate breakfast
• Weighed themselves at least once a week
• Watched <10 hr of television per week

Nutrition for Athletic Performance: Specific Timing Requirements and Recommendations for Optimal Performance

Overview

For peak performance, athletes need to make important decisions regarding the types and timing of food intake as well as the use of supplements. Just as an athlete needs to periodize their physical training, they need to periodize their nutrient intakes to match their daily training, a concept called nutrition periodization. Sport performance and recovery is enhanced with optimal nutrition. It is essential for every athlete to eat a calorically adequate and balanced diet, consisting of a variety of whole foods, on a daily basis. The guidelines presented above for physically active populations are appropriate for elite athletes, however, some specific additional needs for high-performance athletes will be examined in greater detail for the remainder of the chapter.

Canadian Registered Dietitians, with specialized training in sport nutrition, have developed a number of resources for athletes and physically active populations to optimize their nutrition. These tips for training diet, sport specific tips, weight control tips and others are available through the Coaching Association of Canada. To explore these great resources, check out the website at https://www.coach.ca/sport-nutrition-s14783.

When designing meals for athletes, it is important to consider not only what they are eating and the nutrients the foods provide but also the timing of their meals. An athlete who pays attention to meal timing will have sufficient energy to push their limits during a workout and maximize their recovery. They will get the utmost benefit out of every training session and perform their best in competition. Athletes who neglect to pay attention to the timing of their meals often feel tired, lethargic, and experience digestive problems and dehydration. It is important to consider what to eat before, during and after each work-out. Designing the optimal diet plan takes into consideration a variety of factors including the individual athlete, their age, the environment and the type and duration of physical activity  they will be performing. It’s important to note that everyone is slightly different and that the guidelines provide a starting point. The guidelines presented have extensive scientific evidence backing them however, trial and error is necessary to find the optimal nutritional strategy for the individual athlete, which considers both the workout and environmental conditions they will be performing in. In all cases, this trial and error process should occur in training sessions, not during competition. Recommendations for endurance activities will be provided first, followed by recommendations for strength and activities.

Endurance Exercise

Endurance exercise has specific requirements with respect to nutrition due to their high caloric needs. Athletes participating in endurance-exercise perform long bouts of moderate to high intensity exercise and can only do so by carefully planning what they eat before, during, and after their event or training session. Even the leanest of endurance athletes will have sufficient and protein stores to sustain them throughout their physical activity; thus, their primary concern is being able to meet the body’s carbohydrate needs. Energy needs will vary depending on the duration of exercise, the intensity of the exercise, and the athlete’s training and fitness. Protein is primarily important for the recovery, or post-event period.

Pre-event Nutrition

A pre-exercise meal should provide enough energy for the workout without causing any digestive discomfort. Research has shown that eating before exercise improves performance compared to exercising in the fasted state. In the ideal situation, an endurance athlete should have a pre-exercise meal 1-4 hours before their event or training session. Endurance athletes should aim to consume between 1-4 g · kg^-1 BW of carbohydrates in their pre-exercise meal to maintain blood glucose levels and maximize the body’s glycogen stores (Thomas, Erdman et al., 2016). Athletes will need to adjust their pre-exercise meal to match their work-out or competitive event. A longer training session or event will require that the athlete use the high end of the 1-4 g · kg^-1 · BW range. For a shorter work-out or event, athletes should use the low end of the recommended range. Additionally, the athlete’s glycogen stores must be considered. If their glycogen stores are depleted due to a previous work-out, they will be required to use the higher end of the range. The meal should be low in fat and fibre as these nutrients take longer to digest and high intakes have the potential to cause digestive distress. Excess fibre may cause gas production, constipation, bloating and laxative effects. There is some evidence that adding protein to the meal will improve performance in longer endurance events, however, the optimal amount remains to be determined (Jager, Kerksick et al., 2017). Furthermore, the protein content of the meal should be moderate as excess amounts are hard to digest and could promote dehydration. To metabolize protein, the body must cleave the nitrogen containing amino group and eliminate it through the urine. The increased urination increases the risk of dehydration. Finally, it is also important that the pre-exercise meal contains sufficient amounts of fluid as described below.

In the event that a full meal prior to a workout or competition is not possible, as would be the case for an early morning workout, it is essential that the athlete have a complete meal the evening before and an easily digestible snack prior to exercising. Exercising on a full stomach is not recommended; thus, as the time to exercise diminishes the meals should become smaller and easier to digest. Liquids are optimal in this case as they digest more quickly than solid foods and work equally well to promote glycogen resynthesis (Kerksick, Arent et al., 2017). Items like smoothies, sports drinks and meal replacement drinks are very useful and many were developed specifically for athletes. In the event of suboptimal carbohydrate stores pre-exercise, carbohydrate intake during exercise becomes extremely important.

For events lasting longer than 2 hours, athletes can also use carbohydrate loading protocols to maximize their glycogen stores. There are several different protocols for carbohydrate loading; yet, the general technique is a decrease in physical activity and an increase in dietary carbohydrate intake. Many protocols are carried out over a week, but a simpler protocol of 36-48 hours of 10-12 g carbohydrate/kg body weight/24 hour, while tapering training has been found to be equally effective at maximizing muscle glycogen storage (Thomas, Erdman et al., 2016). For athletes undergoing carbohydrate loading, it is important that they also increase their fluid intake because as the body stores additional carbohydrate, it will also store water. As with all sport nutrition, the athlete should test their body’s response to carbohydrate loading prior to their event. For some athletes, carbohydrate loading will make them feel bloated and the benefits of the extra glycogen are outweighed by the weight gain. These athletes may prefer to focus on consuming sufficient carbohydrates during exercise. Athletes exercising for less than 1.5 to 2 hours do not need to carbohydrate load, as they will have sufficient glycogen stores from their normal dietary carbohydrate intake.

Pre-event Hydration

The importance of adequate hydration and electrolyte balance cannot be overstated. Experts agree that a relatively small loss of 2% of body weight can negatively impact physical performance. Realistically, many athletes find it challenging to maintain their hydration status and most cannot consume sufficient amounts of fluid to match their losses when exercising. With this in mind, athletes should ensure adequate hydration prior to commencing a workout. It is recommended that athletes consume 5-10 ml/kg body weight of water or a sports drink 2-4 hours before exercise (Thomas, Erdman et al., 2016). Recommendations based on body weight are much more accurate than providing a universal fluid level for all athletes. The 2-4 hour time period is to optimize hydration status while ensuring that excess fluid can be voided, thereby, preventing the need to urinate during competition. The use of a sports drink will also provide athletes with carbohydrates and electrolytes. Another benefit to a sports drink is that the salts, flavour, and sweetness encourage higher fluid intakes. The use of carbohydrate-electrolyte beverages to stimulate adequate fluid intakes is particularly important during a workout or competitive event. In all cases, consuming a carbohydrate-electrolyte beverage can be a useful strategy for athletes who struggle to consume the recommended amounts of fluid. When planning a hydration schedule, it is imperative to recognize that fluid needs are highly variable and will depend on the athlete and the environmental conditions. All of these factors must be considered and intakes adjusted accordingly.

During Event Nutrition

Regardless of how carefully an endurance athlete plans their pre-exercise meal, it is not possible to physically exert oneself for hours without providing additional nutrients. The general consensus is that any bout of exercise longer than one hour requires supplementary nutrition. As with pre-event nutrition, the focus is on carbohydrates, fluids, and electrolytes as these are the nutrients most likely to limit physical performance when inadequate amounts are available.

Consuming carbohydrates during exercise can vastly improve physical performance. This is critical when an athlete is going into an event or workout with low glycogen stores; this is likely to occur in stage races, tournament situations, or anytime there are repeated exercise bouts with minimal recovery time. For periods of exercise lasting longer than one hour, endurance athletes should consume 0.7 g CHO · kg^-1 · hr during the exercise. For most athletes this works out to 30-60 g CHO · hr^-1. For ultra-endurance exercise, continuous exercise for greater than 2.5 hr, intakes of up to 90 g CHO · hr^-1 are recommended. In this case, the athlete should start consuming carbohydrates shortly after beginning to exercise and approximately every 10 minutes thereafter (Thomas, Erdman et al., 2016, Kerksick, Arent et al., 2017). This schedule is more effective than consuming a single large dose of carbohydrates later in exercise, as it allows for greater stability in blood glucose and maintenance of glycogen stores, as well as minimizing gastrointestinal distress.

There are many ways to obtain adequate carbohydrates during exercise. Athletes should experiment with various strategies during training, to optimize their nutrition for competition. Options include sports drinks, solid food and water, sports gels and water or a combination of these. A sports drink that contains 6-8% carbohydrate is advised, as lower concentrations will not provide enough carbohydrates and higher concentrations will draw water into the gastrointestinal tract from the body. This can lead to both dehydration and abdominal cramping. For this reason, soft drinks, sodas, juice, or other sugar-sweetened beverages are not appropriate choices for fluids during exercise. Importantly, if solid food is to be used, the focus should be on foods that are easy to carry, consume, and digest. It has been suggested that consuming protein during exercise may also be beneficial in endurance events, however, further research is required to confirm the optimal dosage (Jager, Kerksick et al., 2017).

During Event Hydration

For all athletes it is important to hydrate during the event. Given the wide range of environmental and physiological factors that affect an individual’s sweat rate, it is highly recommended that athletes use a personalized fluid replacement strategy rather than a global guideline. Athletes should frequently weigh themselves pre and post exercise to determine their sweat rates and develop appropriate fluid replacement strategies. The goal is to have less than 2% change between baseline body weight and post-exercise body weight (Figure 11-5). Finally, intake of cold fluids (0.5^oC) may help reduce core body temperature when athletes are competing in the heat (Thomas, Erdman et al., 2016).

Athletes can determine their approximate sweat rate by weighing themselves (without clothing), exercising for one hour and then weighing themselves after exercise (without clothing so that the weight of sweat in the clothing doesn’t interfere with the determination). They will also need to keep track of how much they drink during exercise. They can then calculate their sweat rate using the formula below. Recall 1 kg = 2.2 lbs.

Figure 11-5. Sweat rate calculation. Modified from Skolnik and Cherpass, Nutrient Timing for Peak Performance.

Determine pre and post exercise weight

Pre-exercise weight (kg) – post exercise weight (kg) =                         kg lost

                           kg lost

1 000 (1kg = 1000 ml) =                           ml lost

Add amount of fluids consumed during exercise

                            ml lost +                           ml consumed =                          ml sweat lost

This is your sweat rate per hour

*If the athlete urinated during that time, they will need to subtract that amount. It is also important to know that an individual’s sweat rate will change depending on the environmental conditions and the test should be repeated in a variety of conditions.

In events longer than 1 hour, it is recommended that athletes consume fluids that contain electrolytes to ensure adequate replenishment. Specifically, the presence of Na⁺ in the fluid will help stimulate thirst and promote fluid retention. A person can lose up to 1g of Na for every liter of sweat, although this can vary greatly depending on the individual (Sawka, Burke et al., 2007). Athletes need to choose beverages with appropriate electrolyte concentrations to counteract Na⁺ loss in sweat. Practically, an athlete should also be aware of symptoms such as headaches, dark urine, and low urine output, which indicate either a lack of fluid, electrolytes or both (Von Duvillard, Braun et al., 2004). Finally, it is important to note that in some cases it will not be possible for an athlete to consume sufficient fluids during exercise. Typically, the sweat rate exceeds the body’s ability to absorb the required amounts of fluids. In these cases, adequate pre and post hydration are crucial.

Recovery Nutrition

Recovery nutrition depends, not surprisingly, on conditioning, as well as the length and intensity of the exercise session and when the next intense bout of exercise is scheduled. Athletes will have a window of opportunity where they can most effectively recover from their exercise. For speedy refueling, defined as less than 8 hours before the next workout, athletes should aim for 1-1.2g of carbohydrates · kg^-1 body weight · hour^-1 for the first 4 hours followed by their regular meals. Furthermore, maximum glycogen re-synthesis occurs when carbohydrates are consumed within 30 minutes after a workout. Unless the muscles are severely damaged, regular meals and reduced training should restore glycogen levels within 24 hours. It is also important for endurance athletes to consume protein after their workout to provide essential amino acids for muscle repair. For optimal recovery, carbohydrate and protein should be consumed in combination. Ideally, the foods and beverages selected for recovery will provide a carbohydrate, fluid, electrolytes, and protein. See Figure 11-6 for examples of foods and drinks to recover after a workout.

Figure 11-6

Recovery foods. Foods eaten after exercise should provide fluids, carbohydrates, protein and electrolytes

Stage 1: within 30 minutes after exercise

Banana, yogurt, juice

Peanut butter sandwich, strawberries, milk or juice

Flavoured milk, granola bar, apple and water

Sports drink, cheese strings, grapes, juice or water

Low-fat muffin or bagel, homemade smoothie (blend milk, yogurt, fruit, juice and ice)

Protein bar, orange, pretzels and juice or water

Meal replacement drink (Boost^TM, Ensure^TM, etc.), carbohydrate sports bar, apple, water

Stage 2: 1-2 hours after exercise

Meat or cheese submarine sandwich loaded with veggies, milk/juice

Chicken and vegetable stir-fry with brown rice, milk/juice/water

Whole wheat pasta with meatballs, vegetable salad, milk/juice/water

Grilled salmon, quinoa or whole wheat couscous, raw veggies with light dip, milk/juice/water

Bowl of cereal with yogurt or milk, fresh fruit, water/juice

Scrambled eggs with cheese and diced peppers, whole wheat bagel, milk/juice/water

Lentil soup, whole wheat bun, Greek yogurt/regular yogurt, fruit salad, water/soy beverage/milk

Pasta salad tossed with chopped vegetables, canned tuna or chicken breast, milk/juice/water

Cottage cheese or Greek yogurt, fruit salad, low-fat muffin, milk/juice/water

Recovery Hydration

It is not uncommon for athletes to fail to consume sufficient fluids during exercise. To effectively recover from a workout, athletes should weigh themselves pre and post exercise and drink 1.25 L to 1.5 L for every 1.0 kg lost. Aiming to consume this amount of fluid will replace those fluids that are lost through sweating and compensate for fluid lost in urination. It is also advisable with moderate to severe water losses to consume rehydration beverages containing sodium chloride or salty foods to help the body absorb fluids and replace lost electrolytes (Thomas, Erdman et al., 2016).

Strength and Power Training

Strength and activities have specific nutritional requirements that differ from endurance exercise. Carbohydrate needs will be unique and most often lower than endurance activities. Strength and power training also tends to focus more heavily on protein intake with a goal of building and repairing a greater amount of muscle tissue. With all of this in mind, however, it is important to note that carbohydrate intakes are still important during strength workouts and that the average North American diet provides enough protein to meet their needs. With respect to the recommendations, there is overlap in the guidelines for endurance and power training. For example, although strength training will likely have lower rehydration requirements, the process of calculating sweat rates and consuming fluids to replace losses is the same as for endurance activities.

Pre-event Nutrition

Strength training pre-event nutrition should provide sufficient energy to complete the workout or event while not causing any gastrointestinal discomfort. Both foods and fluids are required. The recommendation for a meal consumed 1-4 hours prior to the workout or event that provides carbohydrate at 1-4 g · kg^-1 in combination with some protein is applicable. Carbohydrate intake is still highly relevant, as an athlete that goes into a workout in a state of carbohydrate depletion, will have to rely on other fuels to provide the energy required. A strength training athlete will want to preserve as much muscle mass as possible and does not want muscle protein being metabolized to provide the energy for their workout. For this reason, they will need to consume sufficient carbohydrate to fuel their workout. With respect to protein, whole foods and protein supplements will both be effective as long as high-quality proteins are being consumed. Many athletes choose protein supplements, but there is little to no evidence that they are more effective than protein-containing foods. Supplements also carry with them the risk of contamination with banned substances, which could put competing athletes at risk. Many supplements are also very costly.

During Event Nutrition

Athletes doing a strength and work-out should calculate fluid needs based on their estimated sweat rate (as discussed above). Carbohydrate intakes during resistance exercise are beneficial. Evidence regarding the benefit of a combination of carbohydrates and protein, especially the essential amino acids, is still controversial. Studies do show some benefits however, if adequate carbohydrate is consumed, the additional effect of adding protein is minimal (Jager, Kerksick et al., 2017). Excessive amounts of protein do not enhance muscle and will not digest well causing digestive upset. Excess protein also increases the risk of dehydration due to the need to excrete the unusable nitrogen released with protein breakdown. Furthermore, intakes need to be matched to the amount of energy that is expended during the workout. Regular monitoring of body weight is an effective way to assure energy intake and expenditure are matched. Importantly, excess carbohydrates and protein will result in a gain of mass, not muscle mass.

Recovery Nutrition

A focus on recovery nutrition is essential to achieve maximum benefit from strength workouts. Often the primary goal of a strength workout is to stimulate muscle protein synthesis (MPS), and studies show that exercise will promote MPS for at least 24 hours. Consequently, during the 24 hours post workout athletes will have increased sensitivity to protein intakes. A recovery snack or meal should be consumed as soon as possible after a training session or competitive event. The 30-minute rule mentioned for endurance exercise also applies here. For optimal MPS 0.25 to 0.3 g · kg^-1 BW should be consumed within 2 hours. It is also recommended that protein intakes be spaced out every 3-5 hours and in multiple meals. Protein sources should be high-quality and supplements can be used, if intakes cannot be achieved through whole foods.

Supplements

For optimal performance, athletes are required to be in perfect health and physical fitness. The margin of error between winning and losing is very small and the pressure to win is extreme. As you can imagine, athletes are very interested in any supplement with the potential to enhance their athletic performance and increase their chances of winning. Inherent in a large number of athletes, is the belief that dietary supplements are required to give them a competitive edge and that a “normal” diet will not meet their needs.

Evidence suggests that most legal dietary supplements or ergogenic aids do not improve performance. However, there are a few exceptions to this. The most conclusive evidence exists for the use of creatine in short-power events, and caffeine during endurance events. There is also some evidence that sodium bicarbonate can be beneficial due to its ability to offset the decrease in blood pH, which occurs with physical activity. However, sodium bicarbonate is also associated with adverse gastrointestinal side-effects including diarrhea. Finally, dietary nitrates may enhance muscle function and increase blood flow. Other supplements such a carnitine, chromium, coenzyme Q10, and oxygenated water have not been found to enhance physical performance (Maughan, Burke et al., 2018).

Another concern with athletes and supplement use is the risk of inadvertently consuming a substance that is on the banned substance list. In this case, it could be deliberate or accidental. In either circumstance, the athlete is blamed and their awards can be withdrawn and sanctions imposed. Doping is a serious offense for an athlete and can be career-ending. It is extremely important for all athletes to be aware of the rules and make sure they follow them. This is difficult if they are consuming a product with unknown composition. You can get more information on doping regulation by going to the Canadian Centre for Ethics in Sport website: www.cces.ca.

Dietary and sport supplements can be beneficial for many athletes, particularly if the athlete has a nutrient deficiency that needs to be corrected. Products like sports bars and drinks are specifically designed to meet the athlete’s needs and are easy to carry and drink or eat. They do tend to be expensive, however, and in most cases a well-planned diet can meet most of the athlete’s needs. All athletes must be sure that the products they consume are permitted in their sport and that they are not contaminated with any banned substances. Several studies have tested the contamination of supplements and find that between three and 25% have steroids or stimulants not listed on the label (Judkins, Teale et al., 2010). Product purity can be ensured by using supplements that have been evaluated by an independent laboratory that certifies them as contamination free and appropriate for athlete use. One supplement company that verifies their product via independent testing is NSF International. NSF International has a NSF Certified for Sport Program. More information can be found at their website: www.nsfsport.com.

Summary

Physically active individuals and athletes alike require adequate intake of the six essential nutrients: carbohydrates protein, , vitamins, minerals, and water. This ensures that all bodily processes are maintained, and adequate energy production can occur. The AMDR recommends 45-65% of kilocalories come from carbohydrates (4 kcal/g) and that athletes should strive for 3-12 g · kg^-1 of body weight from carbohydrates depending on exercise duration and intensity. This ensures adequate energy for storage as blood glucose and glycogen. When carbohydrate intake is insufficient, individuals do not have adequate energy for intense physical activity. Protein (4 kcal/g) is required for energy supply and for replacement/production of bodily proteins. The AMDR for protein is 10-35% of daily energy intake or specifically 0.8-2.0 g· kg^-1 of body weight depending on activity levels. Most Canadians consume adequate protein with their daily diet and do not require protein or amino acid supplementation. The third macronutrient, fat (9 kcal· g^-1 is recommended to provide 20-35% of energy intake with no more than 10% from saturated fats. Dietary fat is required for many functions including energy production during low intensity physical activity. In addition to the three energy-providing macronutrients, we also require vitamins and minerals for wellness and optimal performance. Vitamins are organic substances required in relatively small amounts. For physically active individuals and athletes, the B vitamins, vitamin D, and the antioxidants (C and E) are particularly important. The B vitamins are critical in energy metabolism; vitamin D is important for bone health; and the antioxidants help to maintain balance with free radicals. Similar to vitamins, minerals are also required in small amounts, but are inorganic substances. Physically active individuals and athletes should be most concerned with adequate intake of zinc, iron, calcium and the electrolytes, sodium, potassium, and chloride. When individuals consume a calorically adequate and balanced diet, supplementation with vitamins and minerals is generally not recommended. A supplement will not compensate for a poor, insufficient diet and there is little evidence that high-dose vitamin or mineral supplementation will improve performance, in the absence of a deficiency. Water is the sixth essential nutrient and is critical for performance. Individuals should maintain water balance during physical activity to prevent dehydration-induced deterioration of performance.

Understanding energy requirements is critical in optimizing athletic performance. This includes both energy balance and the timing of specific nutrient intake. Energy balance occurs when energy intake is equal to energy expenditure, over a fixed period of time. A negative energy balance results in weight loss, whereas positive energy balance results in weight gain. Negative energy balance can result in conditions such as the triad and a positive energy balance can result in excess gain. By understanding energy needs, one can estimate how to achieve a healthy body weight and maintain or obtain a body weight that optimizes athletic performance. In addition to consuming adequate amounts of nutrients, athletes should be aware of when they are consuming foods and fluids. The pre-race nutritional strategies of athletes can involve many unique strategies such as carbohydrate loading, pre-event meals, and pre-event snacks. During an event, an athlete must consider both energy requirements and fluid/electrolyte needs based on duration, intensity, and other personal factors. Finally, after training or a competitive event, athletes require adequate recovery nutrition to ensure that they will be ready to perform at subsequent events.

Exercises or Topics for Discussion

• Design a dietary strategy for a 25-year-old male (70kg) who is completing his first marathon (42.2km road race). Include strategies for pre-race preparation, during race requirements, and post-race recovery. Ensure that both fluids and energy requirements are met.
• If this was a multi-stage event where the athlete was required to run a total of 250 km over 5 consecutive days, how would the dietary strategy for optimum performance be changed?
• Discuss the safety and efficacy of ergogenic aids in sports performance.
• Discuss how the 6 nutrients work together to provide an athlete with sufficient energy for physical activity. What can happen with a diet that is calorically inadequate or nutritionally unbalanced?

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About the Authors

Raylene A Reimer, PhD, RD
Professor, Faculty of Kinesiology, University of Calgary
Department of Biochemistry & Molecular Biology, Cumming School of Medicine
Full Scientist, Alberta Children’s Hospital Research Institute

L.K. Eller, Faculty of Kinesiology, University of Calgary

For over 15 years, Lindsay Eller has enjoyed various teaching and research roles in the Faculty of Kinesiology at the University of Calgary.  Currently, Lindsay coordinates various clinical trials examining the role of the microbiome in both disease and healthy states.   When not at work, she enjoys spending time skiing and climbing in the Rocky Mountains.

J.A. Parnell, Department of Health, and Physical Education, Mount Royal University

Dr. Parnell is an Associate Professor at Mount Royal University in the Department of Health and Physical Education. She teaches courses in nutrition, research methods and statistics, and physical literacy. Her research encompasses diverse athlete populations including youth athletes, Paralympic athletes, and endurance runners with a focus on diet quality, ergogenic aids, and exercise induced gastrointestinal symptoms.